Structural and dielectric/ferroelectric properties of (La1-xNdx)(2)Ti2O7 synthesised by sol-gel route (original) (raw)
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Structural and dielectric/ferroelectric properties of (La1−xNdx)2Ti2O7 synthesized by sol–gel route
Journal of Solid State Chemistry, 2010
A series of compounds with the general formula (La 1 À x Nd x ) 2 Ti 2 O 7 (0.0 r xr 1.0) has been prepared by the sol-gel method. The decomposition of the gel was characterized by thermo-gravimetric analysis coupled to mass spectrometry, indicating the reaction is achieved above 850 1C. The lattice parameters versus x show an expected decrease in the a and b parameters while c and the b angle remain almost unchanged with respect to the monoclinic symmetry conserved for the full solid solution. Dielectric, piezoelectric and ferroelectric properties were measured on the entire series.
Study on properties of tantalum-doped La 2 Ti 2 O 7 ferroelectric ceramics
Journal of Advanced Dielectrics, 2015
A series of ceramics with a general formula, La 2 Ti 2Àx Ta x O 7 , in which x ¼ 0:05; 0:1; 0:2; and 0.3, were prepared by Spark Plasma Sintering (SPS). Effects of tantalum substitution for titanium on the structure, dielectric, and piezoelectric properties were studied. Results revealed that the structure changed gradually from 4-layer to 3-layer due to the higher valence of Ta. The solid solution limit of tantalum in La 2 Ti 2 O 7 lattice was in the proximity of x ¼ 0:2. The ferroelectric Curie temperature (T c ) decreased with increasing tantalum doping content. dc resistivity reached a maximum value at x ¼ 0:2 with a value of $ 1:0 Â 10 8 Á cm at 600 C. The influence of texture on the piezoelectric properties of La 2 Ti 2Àx Ta x O 7 ceramics was also investigated. A maximum d 33 value $ 2:1 pC/N was obtained at x ¼ 0:2.
Enhanced electrical properties of La1.9Nd0.1Ti2O7 ceramics
Journal of Materials Science: Materials in Electronics, 2019
La 2−x Nd x Ti 2 O 7 (LNTO) ceramics with enhanced electrical properties have been prepared by traditional solid-state reaction method. The LNTO ceramics maintain a pure monoclinic phase at x ≤ 0.1. At x > 0.1, an orthorhombic phase Nd 0.95 TiO 3 appears. Impedance spectra indicates that the substitution of La 3+ ions by Nd 3+ ions at A sites generates defects, resulting in the enhanced distortions of TiO 6 octahedrons. The dielectric relaxation activation energy for these defects is 1.2 eV in temperature range T ≥ 650 ℃. The conductance activation energies are 0.3 eV and 1.0 eV for impure ions/thermions and defects/oxygen vacancies, respectively. The contributions of impure ions/thermions and defects/oxygen vacancies have been distinguished through the analysis of both normalized imaginary impedance Z″ and electrical modulus M″. Their impedance relaxation activation energies in normalized Z″ spectra are 1.3 eV and 0.8 eV, respectively. An enhanced piezoelectric coefficient (d 33 = 2.8 pC/N) appears in La 1.9 Nd 0.1 Ti 2 O 7 (LNTO-0.1) ceramics.
Synthesis, structure and dielectric characterization of Ln2Ti2−2xM2xO7(Ln=Gd, Er; M=Zr, Sn, Si)
Materials Research Bulletin, 2002
The progress in wireless communications and information access has demanded the use of electronic ceramics exhibiting desired properties. To further our understanding of these properties, compounds in the Ln 2 Ti 2±2x M 2x O 7 (Ln Gd, Er; M Zr, Sn, Si) systems were synthesized by ceramic methods and characterized by powder X-ray diffraction. The ZrO 2 ±doped Gd 2 Ti 2À2x Zr 2x O 7 compounds adopt the pyrochlore structure type and form a complete solid solution. Er 2 Ti 2À2x Zr 2x O 7 forms a pyrochlore solid solution for x < 0:1. However, stoichiometric Er 2 Zr 2 O 7 does not form; instead Er 4 Zr 3 O 12 forms a with defect uorite structure. The Sn±doped Ln 2 Ti 2À2x Sn 2x O 7 (Ln Gd, Er) compounds form complete solid solutions, and the Si compounds adopt the pyrochlore structure up to x 0:05. At ambient temperature, dielectric constants range from 10 to 61 for Er 2 Ti 2À2x Zr 2x O 7 and 16±31 for Gd 2 Ti 2À2x Zr 2x O 7 with low dielectric loss (1 Â 10 À3 ) at 1 GHz. #
Microstructural characterization of sol–gel derived Pb1−xLaxTiO3 ferroelectrics
Journal of Alloys and Compounds, 2005
The ferroelectrics Pb 1−x La x TiO 3 with good stoichiometry were prepared by a sol-gel route in the composition range from x = 0.0 up to 0.4 in 0.05 increment. The compounds were indexed in a tetragonal phase for 0.0 ≤ x < 0.25, and in a cubic phase for 0.25 ≤ x < 0.4. A tiny amount of pyrochlore phase La 2 Ti 2 O 7 was detected at x = 0.4. The ion oxidation states of solid solution compounds were characterized by X-ray photoelectric spectroscopy (XPS) and electron spin resonance (ESR). For the compounds Pb 1−x La x TiO 3 prepared in the atmosphere, the electrical neutrality is kept not by the reduction from Ti 4+ to Ti 3+ , but by the creation of cation vacancies in the A-and B-sites. The grain size of Pb 1−x La x TiO 3 increases with increasing La content.
Korean Journal of Chemical Engineering, 2004
Amorphous La 2 O-TiO 2 powders were synthesized by the polymerized complex (PC) method. The activation energies for crystallization and grain growth of La 2 Ti 2 O 7 from these precursors were determined from results of XRD and DTA and compared with those for La 2 Ti 2 O 7 precursors by the conventional solid-state reaction (SSR). Activation energy of grain growth of La 2 Ti 2 O 7 in PC-sample was determined to be 7.1 kJ/mol while that of SSR sample was 14.8 kJ/mol. The energy required for the phase transformation from amorphous PC sample to layered perovskite was 432 kJ/mol, while the SSR sample did not show this transition below 900 o C. It was clearly demonstrated that the La 2 Ti 2 O 7 crystals were formed at a lower temperature and they grew in size faster in the sample prepared by the PC method relative to the sample prepared by the SSR method. Mixing of elements in molecular level in PC preparation appeared responsible for these differences.
SYNTHESIS AND DIELECTRIC PROPERTIES OF La0.67LixTi1-xAlxO3 (0.15≤x≤0.3) CERAMICS
Ukrainian Chemistry Journal, 2020
Solid solutions of Al-doped lithium lanthanum titanates La0.67LixTi1-xAlxO3 system (where 0.15 ≤ x ≤ 0.3) have been synthesized by solid-state reaction technique. Light optical microscopy has shown that the grain size of La0.67LixTi1-xAlxO3 ceramics insignificantly increases with an increase in lithium/aluminum concentration. The materials La0.67LixTi1-xAlxO3 show very high dielectric permittivity ε΄ 104 over a relatively wide frequency range (102 ≤ f ≤ 104 Hz) with no apparent dependence on the x. The impedance spectroscopy study indicates three semicircles on Cole-Cole diagram that can be attributed to electrically different areas of ceramic’s grain.
Room-temperature ferromagnetism and ferroelectricity of nanocrystalline La2Ti2O7
Journal of Alloys and Compounds, 2010
ABSTRACT La2Ti2O7 nanocrystalline powders and pellets were prepared by sol–gel method. The nanocrystalline powders present room-temperature ferromagnetism (FM). The vacuum annealing enhances FM, showing that the observed room-temperature FM for La2Ti2O7 possibly originates from oxygen vacancies at/near surfaces of nanograins. La2Ti2O7 pellets annealed at 1000 °C for 1 h show the coexistence of ferromagnetism and ferroelectricity (FE) at room temperature. Meanwhile, the room-temperature magnetodielectric (MD) effect was also observed in the La2Ti2O7 multiferroic pellet, indicating the coupling between magnetic and electric properties. The value of Δɛr/ɛr(0) for La2Ti2O7 multiferroic pellet reaches 39.3% at 1 kHz under H = 6 kOe.